Sanke Keg/Manifold/"D" Coupler Co2 Leak

Hey guys,

I have had a Co2 leak on my system that I have tried to diagnose for weeks and I simply cannot figure it out. The situation is essentially as follow: I am running 3 sanke kegs from a 4 port manifold, which is in turn connected to the output of my regulator. The sanke kegs all use commercial style "D" couplers. When I pressurize the system, close the ball valves on the manifold, and shut off the pressure from the Co2 tank to the regulator, I lose no pressure over a 48 hour period. When I pressurize the system, open the manifolds, thus sending Co2 to the kegs, and shut off the Co2 tank, the system goes to 0 PSI after 6 - 12 hours. This should mean that the Co2 leak is after the manifold. Now, I took the following steps to locate the leak, to no avail:

1. Submerge manifold in water to find bubbles. No bubbles, even after 2 minutes of watching;
2. Leak test regulator output. No leaks. I even retaped the connection anyway and tested again;
3. Leak test all "D" couplers. I performed this leak test by submerging the coupler in water with the system pressurized. I found no gas leaks, even around the pressure relief valve and Co2 connections;
4. Leak test sanke kegs. I performed this leak test by filling the top of the sanke keg with water to see whether the valve might have a slow leak. Again, no bubbles; and
5. Leak test sanke kegs with D couplers installed. I wanted to see if the sanke kegs leaked only when the coupler was installed. For this, I filled the top with water to see if gas leaked from around the edges of the coupler while installed on the keg. No leaks.

I have no idea what to do from here and any suggestions would be fantastic. This sounds absurd, but the only thing I can think of is that the hoses themselves are losing pressure, because all the connections appear to be airtight. Is this even possible?

 

The one time I had a leaking sanke keg, it leaked around the area where the retaining clip goes. In your leak test are you filling to the absolute very top so that even the retaining clip area is covered? I was able to detect mine by spraying starsan and observing the bubbles. Side note but in my case the leak was my fault because I tried to close up the keg with light fishing line hanging out and connected to a dry hop bag.

 

That is correct - the water level is over the retaining clip. I even attach the coupler and fill the water level over the retaining clip and look around the perimeter of the coupler and even then see no bubbles, just in case the leaks happen only when the coupler is attached. Like I said, I would be grateful if anyone could help me figure it out because it is a doozy!